As shown in FIG. 1, a conventional dual cladding fiber (DCF) has an internal structure typically consisting of a core 100, an inner cladding 102, an outer cladding 104, and a protection jacket 106. Both the core 100 and inner cladding 102 are structured to guide an optical wave along a longitudinal axis 108. A wave guiding mechanism is provided either by total internal reflection through an appropriate refractive-index profile (see FIG. 1) or Bragg band gap properties. The core 100 can typically be designed to guide only a single spatial mode, so called HE11 mode. The inner cladding 102 can guide hundreds to millions of multiple spatial modes. The DCF have been developed originally for optical fiber amplifiers and lasers. Signal light propagating in a rare-earth-ion-doped core of the DCF can be amplified while interacting with pump waves guided in the cladding. Recently, it was demonstrated that DCF can be applied in biomedical imaging. In particular, the probe light is delivered through the single-mode core to a biological sample, whereas the signal light transmitted through or reflected from the sample can be collected by the inner cladding as well as the core of DCF. This exemplary arrangement can be advantageous over more conventional method based on a single-mode fiber or multi-mode fiber in terms of spatial resolution, light collection efficiency, etc.
In such applications using the DCF, an arrangement or a technique to launch or extract light in and out of either only the core or the inner cladding of the DCF can be used. Conventional arrangements generally include free-space optics. As shown in FIG. 2, the core mode in a DCF 110 is transmitted to the core 100 of a first receiving fiber 112 through lenses 113, a beam splitter 114, and a pinhole 115. The cladding modes of the DCF 110 are received by a second fiber 117 through a beam blocker 118. However, this conventional arrangement may suffer from significant insertion loss due to beam splitting and mode profile mismatch.
Accordingly, there may be a need to address and/or overcome at least some of the deficiencies described herein above.